Aha! very confusing.
I think you have the same LCD as me, they are wired differently to most others, and I got mine going more or less by accident.
7．LIGHT--------- backlight control terminal
Is just a rather pompous way of saying LED to ground. Just do it and it will be fine.
My displays are on shields, so I can't test anything. If it works without ground pin 8 connected, I guess it is getting a ground through pin 7 LED. I guess it will stop if you disconnect pin 7 too
As for the second question, it is garbled, but perhaps the above answers it. It's not clear if your PWM control works at all, I assume it doesn't. If that is the case, I wouldn't bother anyway. This particularly applies if the backlights are blue. They are so useless you are likely to find they are better left disconnected.